A traditional light emitting diode driver is depicted in FIG. 3. As shown therein, the level control signal 30 determines the final level of the current 1 in the light emitting diode 21. If the signal feedback 4 from the photo diode 23 to the comparator 5 is less than the level control signal 30, the comparator 5 sends an increased signal 6 to the operational amplifier 12 which buffers the increasing signal to the current source 10, which increases the light emitting diode 21""s radiant output 22 which finally increases the feedback signal 4 until it equals the level control signal 30.
In one aspect of the invention, there is described a light emitting diode driver arranged to supply a drive current to a light emitting diode, the light emitting diode arranged with a photo detector that forms a monitor signal based on a radiant output that is formed by the drive current and the light emitting diode, the drive current comprising a first current and a second current and formed by comparing the monitor signal and a level control signal to form a comparison signal; providing a buffered output signal based on the comparison signal; providing a voltage difference based on the buffered output signal and the drive current""s nodal voltage; forming a first current based on the voltage difference and a resistor; providing an amplified signal based on the voltage difference; and providing the second current based on the amplified signal.
In another aspect of the invention, there is described a light emitting diode driver arranged to supply a drive current to a light emitting diode, the light emitting diode arranged with a photo detector that forms a monitor signal based on a radiant output that is formed by the drive current and the light emitting diode, the drive current comprising a first current and a second current; the first current formed by a voltage difference across a resistor; the voltage difference formed by drive current""s nodal voltage and the high speed buffer output; a high-speed buffer output formed by a comparison signal; a comparison signal formed by comparing the monitor signal and a level control signal; and the second current provided by a current source whose input terminal is driven by an operational amplifier, the operational amplifier having an input signal that is the voltage difference formed by drive current""s nodal voltage and the high speed buffer output.
In a further aspect of the invention, there is described an image forming device comprising a light emitting diode driver, the light emitting diode driver arranged to supply a drive current to a light emitting diode, the light emitting diode arranged with a photo detector that forms a monitor signal based on a radiant output that is formed by the light emitting diode, the drive current comprising a first current and a second current and formed by comparing the monitor signal and a level control signal to form a comparison signal; providing a buffered output signal based on the comparison signal; providing a voltage difference based on the buffered output signal and the drive current""s nodal voltage; forming a first current based on the voltage difference and a resistor; providing an amplified signal based on the voltage difference; and providing the second current based on the amplified signal.
In yet another aspect of the invention, there is described an image forming device comprising a light emitting diode driver, the light emitting diode driver arranged to supply a drive current to a light emitting diode, the light emitting diode arranged with a photo detector that forms a monitor signal based on a radiant output that is formed by the light emitting diode, the drive current comprising a first current and a second current; the first current formed by a voltage difference across a resistor; the voltage difference formed by drive current""s nodal voltage and the high speed buffer output; a high-speed buffer output formed by a comparison signal; a comparison signal formed by comparing the monitor signal and a level control signal; and the second current provided by a current source whose input terminal is driven by an operational amplifier, the operational amplifier having an input signal that is the voltage difference formed by drive current""s nodal voltage and the high speed buffer output.